A characteristic need for most ring laser gyros is that the path length of the laser cavity needs to be changed to optimize laser efficiency through an automatic path length control. In a form of this control, a modulation signal is added to a signal that controls transducers to change the path length as a function of laser power. This modulation signal inherently modulates the laser by modulating the path length. This modulation signal is used to demodulate an output of the gyro which is proportional to the deviation from maximum laser power within the gyro, and produce a signal that is integrated by an integrator to drive the transducers. The greater the amplitude of this modulation, the faster the automatic path length control can acquire the point of maximum laser power. But once the point of maximum laser power is found, the modulation results in a deviation from this point of maximum laser power, with the larger the modulation, the larger the deviation from this point of maximum power. Consequently, it is desired for optimum gyro performance, to have a large modulation signal when trying to acquire the point of maximum laser power and to have a small modulation when operating at the point of maximum laser power.
In most applications of this automatic path length control, there are multiple drive levels to the path length control transducers that result in points of maximum laser power within the control range authority of the path length control. The integrator has to be reset periodically to a point closer to the center of the control range authority to avoid saturating the path length control. Since this reset of the integrator usually results in the path length control operating away from a point of maximum laser power, it is desired to reacquire another point of maximum laser power as fast as possible, which maximizes gyro performance by minimizing the time spent operating away from a point of maximum laser power. Once another point of maximum laser power is acquired, it is desired to reduce this modulation to an amplitude that is low enough to cause negligible degradation in gyro performance due to the modulation while still being large enough to allow automatic path length control to remain at this newly acquired point of maximum laser power.